The present invention relates to an apparatus and method for a fast changeover in a duplex system, and more particularly to an apparatus and method for a fast changeover in a duplex system, by which one system is changed over fast to the other system when either of one system of a duplex system in an optical CATV system fails.
In a conventional changeover method for a duplex system, to verify the state of a self side in an active state, the information of a pair side is stored in a particular area of a register or a memory, and the content stored in the memory area is accessed in a polling manner to interpret a state so that restoration operation is processed according to a fail state of the system. However, using the above conventional method causes a complicated structure of a processor and other circuit to recognize the pair state, and also, requires lots of manufacturing cost. Also, when multiple units or groups are to be checked, the whole system breaks down before being changed over due to a low processing speed. Thus, the liability of the duplex system becomes low, and the expansion of a large system, such as an optical CATV, becomes impossible.
On the other hand, as a changeover technology used for CATV, there is one for example that is disclosed in U.S. Pat. No. 5,253,309. The disclosed optical system includes at least one optical input port for receiving an optical signal from an optical source, a modulation port for receiving the optical signal from the optical source, an optical modulator having complementary output ports, and an optical source, wherein complementary modulated output signals are applied at least to a single optical receiver at the other end of an optical transmission link. This is for maintaining a particular level by modulating an optical signal into a complementary form in the optical modulator to reduce the S/N ratio of the system, and separately providing the modulated signal to two separate optical receivers.
In an embodiment, two complementary signals are provided to the separate optical receivers, or to a signal balanced receiver, thereby an optically modulated signal is modulated. The S/N ratio is increased by doubling a signal level. In the embodiment, a signal optical transmission channel is used, and the two optically modulated signals are separated in polarization so as to be capable of being separately detected on the receiving end of the link, and feedback means is used to insure proper polarization state for the two complementary signals.
However, the aforesaid changeover technology is for separating a signal itself, thus, the technology cannot be applied to a changeover technology where a signal itself is exchanged.